Fluid pressure actuated switch



May 27 1952 G. H, HANSEN FLUID PRESSURE AGTUATED SWITCH 2 SHEETS--SHEET l Filed April 8, 1950 s. y 5 3 M N g w m m i .l riL f`. Q. 7.. 2f. w...)

May 27, l952 G. H. HANSEN 2,598,536

FLUID PRESSURE ACTUATED SWITCH Filed April 8, 1950 2 SHEETS-SHEET 2 60 Afro/@N545 Patented May 27, 1952 FLUID PRESSURE ACTUATED SWITCH Gilbert H. Hansen, Batavia, Ill., assigner to Furnas Electric Company, Batavia, Ill., a corporation of Illinois Application April 8, 1950, Serial No. 154,799

My present invention relates generally to improvements in electric switches, and relates more specifically to various improvements in the construction and operation of fluid pressure actuated electric toggle switch assemblages.

The primary object of the present invention is to provide an improved fluid pressure actuated electric switch which is simple and compact in construction, and which is moreover highly efficient in operation.

Many different types of fluid pressure operated electric switches have heretofore been proposed and utilized for diverse purposes, and in some of these prior switch assemblages the contacts were presumably opened and closed with a snap action by means of toggle and spring mechanism activated by variations in the pressure of the operating fiuid. In the prior toggle switches most extensively used, the contact actuating toggle links were rigid and were snapped from one extreme position to another with the aid of coil springs, and in these mechanisms the rigid toggles would frequently hang on dead center thus making it difficult to obtain the impact blows necessary for positive and quick closing and separation of the switch contacts. Then too, the prior rigid toggle mechanisms would tend to wear rapidly and thereby introduced inaccurate functioning of the switches, andthey also failed to insure sufficient contact closing pressure so as to properly carry the starting current of the motor or other equipment with which the switches were associated. These prior switches were also objectionable due to their relatively complicated construction, and because of the fact that adjustment of the actuating vpressure ranges could not be accomplished with sufficient precision, thus making the prior fluid. pressure actuated switches unsatisfactory for diverse reasons.

It istherefore an importantV object of my present invention to provide an improved snap-action toggle switch which obviates all of the abovementioned objectionable features, and which emv bodies a highly sensitive and reliable actuating toggle mechanism.

Another important object of this invention is to provide a simplified and durable spring toggle assemblage, which will insure proper snap-,act1on of the relatively movable switch contacts so as to positively close and open these contacts at all times and while under the influence of variable fluid pressures.

A further important object of the invention V1s to prov-ide an improved multiple leaf-spring toggle ymechanism for fluid pressure actuated 18 Claims. (Cl. 20D-81.5)

2 switches, wherein the resilient toggle links or elementsy will definitely produce the hammer blows requisite in order to assure suicient snapaction at the contacts, regardless of the position or setting of the pressure range varying mechamsm.

vStill another important object of my invention is to provide an exceedingly compact pressure actuated switch assembly comprising a relatively few simple but sturdy parts, which may be readily constructed, assembled and dismantled, while also being safely conveniently vaccessible for inspection and adjustment.

An additional important object of the present invention is to provide a toggle switch operable by fiuid pressure, wherein sufficient adjustment is provided for normal wide ranges of variation of differential and pressure settings, and which will also amply compensate for inaccuracies such as might result from mass production of parts.

Another important object of this invention is to provide an improved switch toggle mechanism in which the toggle elements are adapted t0 be snapped into operating position and are maintained in such position without the aid of additional fastening means, and wherein the parts are constructed of durable special materials capable of most effectively resisting undesirable wearrand tear. f

A further important object of my present invention is to provide an improved well insulated electric switch unit of utmost precision and dependability having all elements amply protected against damage, and which may be manufactured and sold for. diverse uses at moderate cost.

'IThese and other more specific objects and advantages of the invention will be apparent from the following detailed description.

A clear conception of the novel features constituting my present improvement, and of the construction and operation of a typical fluid pressure actuated switch unit embodying the same, may be had by referring to the drawings accompanying and forming a part of this specication and wherein like reference characters designate the same or similar parts in the various' sure actuated switch units with the top cover removed; j

Fig. 2 is a central longitudinal section through the completely assembled unit, the section havingV been taken along the line 2-2 of Fig. l;

Fig. 3 is a side elevation of the same switch unit but with the casing, cover and fluid pressure applying mechanism omitted;

Fig. 4 is an end View of the portion of the switch unit shown in Fig. 3, with a portion of the guard plate broken away;

Fig. 5 is an opposite end view of the same portion of the mechanism which is shown in Fig. 3;

Fig. 6 is a reduced transverse section through the terminal block or board of the switch, taken along the line 6-6 of Fig. 3;

Fig. 7 is a similarly reduced transverse section through the terminal board of the unit, taken along the line 1-1 of Fig. 3; and

Fig. 8 is a reduced top view of the fluid pressure transmitting stirrup and its retainer element.

The gist of my present invention is the provision of a highly sensitive and dependable leafspring toggle for insuring positive closing and opening of the contacts of a fluid pressure actuated switch with an impact snap-action, and While the invention has been shown by way of illustration as being advantageously applicable to a double-contact electric switch unit for controlling the starting and stopping of a motor, it is not my desire or intent to unnecessarily re strict the utility of the improved features by virtue of this limited embodiment. It is also contemplated that specific descriptive terms employed herein be given the broadest possible .in-

terpretation consistent with the actual disclosure.

Referring to the drawings, the improved fluid pressure actuated electric toggle switch unit shown therein comprising in general, a main frame I having a base I I provided with integral opposite side walls I2 and an intervening end wall I3; a rigid lever I4 having one end portion provided with integral side pivots I swingably coacting with notches I6 in the side walls I2 of the frame ID while its opposite swinging end is provided with laterally spaced hooks I1; a exible diaphragm I8 cooperating with a stirrup plate I9 having upstanding side projections coacting with sockets formed in the medial portion of the lower face of the lever I4; an elongated stifened toggle plate 2l having a longitudinal edge 22 swingably cooperable with the hooks I1 of the lever I4; a flexible toggle link or leaf spring 23 pivotally coacting with each ets 25 formed in the frame wall I3; a terminal board 26 firmly but detachably secured to the ends of the frame walls I2 remote from the base II by means of screws 21, and having two lixed contacts 28 mounted thereon above the hooks I1; movable contacts 29 carried by spring arms 30 secured to the board 26 remote from the fixed contacts 28 but being cooperable with the latter; a reciprocable rod or bar member 3i operatively connecting the swinging medial portion of the toggle plate 2I with the movable contact carrier arms 30 near the contacts 29; and an adjustable compression spring 32 coacting with the medial portion of the upper face of the lever I4.

fThe main frame I with its integral bottom II, side walls I2 and end walls I3 may be formed of a single piece of sheet metal with the aid of punches and dies, and the terminal board 25 which spans and is rmly but detachably secured to the yframe walls I2 by means of the screws 21, is formed of insulation and provides a rigid connection between these walls I2. The frame I0 and contact carrier board 26 may be housed as a unit within a durable sheet metal casing 34 having therein one or more openings 35 for the electrical conductors, and the flexible diaphragm I8 may be firmly clamped to the bottom of the housing 34 by an enclosure 35 held in place by the same screws or other fasteners which normally hold the frame I0 in proper position within the casing 34. The casing 34 is also preferably provided with a durable sheet metal cover 31 which may be detachably secured to the terminal board by means of a single stud 33 coacting with a threaded opening 39, and the lower enclosure 36 cooperates with a pulsation eliminator 4B and with a fluid supply nut 4I to provide a fluid pressure chamber 42 beneath the flexible diaphragm I8, see Figs. 1 and 2.

The rigid lever I4 and the uid pressure transmitting stirrup I9 may also be formed of durable relatively heavy sheet metal with the aid of punches and dies; and besides the pivots I5 which coact with the frame sockets I6 and the hooks I1, the lever I4 has a central depression 44 formed therein for the reception of the adjacent end of the spring 32. The downwardly open sockets with which the knife edges at the free upper ends of the stirrup projections 20 coact, are disposed in opposite sides of the depression 44, and the stirrup plate I9 is provided with a thin and highly flexible sheet metal retainer element 43 secured centrally thereto and coacting with the frame base, see Figs. 2 and 8. The extreme end of the lever I4 remote from the hooks I1 is provided with an integral shelf 45 which is adapted to coact with a flange formed on the lower end of a U-shaped stop member 46 the upper end of which is provided with a similar fiange with which an increment differential adjusting screw 41 has screw thread coaction. This screw 41 extends loosely through a hole 48 formed in the terminal board 25 and is surrounded by a helical compression spring 49 coacting with the screw head and which constantly urges the stop element toward the terminal board 26 with any desired force dependent upon the adjustment of the screw 41; and this screw is readily accessible for manipulation upon removal of the cover 31, see Figs. l, 2 and 3. The screw 41 may be held in adjusted position by a U-shaped spring clip 50 the opposite sides of which spread while an adjustment is being effected but will normally prevent turning of this screw.

The improved snap-action toggle consisting of the toggle plate 2| and the toggle leaf springs 23 constitute an important feature of my invention, and this toggle is operable by the movement of the rigid lever I4 in opposite directions to positively deliver hammer blows or impacts to the movable contacts 29 when moving in either direction. The toggle plate 2| which is swingable relative to the lever hooks I1 on the knife edge 22, is preferably formed of thin and rigid sheet steel and is stiiened along its medial portion by a longitudinal corrugation 52 as shown in Figs. 2, 3 and 5. The elongated toggle leaf springs 23 are straight before insertion but are thereafter longitudinally curved and are preferably formed of relatively thin spring bronze, and while the rear ends 24 of the toggle springs 23 are snugly seated within the frame sockets 25, the front ends 53 thereof are bent to interlock with slots formed in the adjacent end portions of the The contacts 28, 29 will remain open as long as the high pressure is maintained within the chamber 42, but when this pressure drops sufficiently so that the spring 32 overcomes the diaphragm lifting effect, then the lever I4 will swing downwardly about its pivot projections I5. This downward swinging of the lever I4 carries the connection between the toggle springs 23' and the toggle plate 2I upwardly and stresses the leaf springs 23 until the toggle link connection again crosses dead center, whereupon the springs 23 immediately become effective to snap the toggle upwardly into its extreme uppermost position. During this rapid upward flexing of the toggle, the bar member 2l will again receive a hammer blow from the projection 64 of the toggle plate 2|, thus producing impact closing of the movable contacts 29 and stressing the resilient movable contact carrying arms 30 sufficiently so that they will bend and produce a desirable wiping action upon the fixed contacts 28. This stressing of the spring arms 30 positively prevents rebound of the movable contacts 29 and also augments subsequent opening motion thereof.

Both the opening and closing of the contacts 28, 29 are thus effected rapidly, positively and with a decided snap and wiping action, and without permitting the toggle links to hang on dead center; and whenever the lever I4 is swung upwardly about the projections I5, the rear shelf of this lever will swing downwardly so as to engage the lower flange of the bracket 46. This engagement causes the U-shaped bracket 4B to move downwardly and to compress the spring 49, and the force exerted by this spring 49 aids the main spring 32 in opposing the fluid pressure so that greater uid pressure is required to open the contacts than if the spring 49 were omitted.

The screw 41 may be adjusted to vary the bracket retaining pressure and the degree of compression of the spring 49, thereby increasing or decreasing the pressure differential accordingly, and the main heavier spring 32 may be adjusted by manipulation of the adjusting screw 14 so as to l simultaneously vary both the contact opening and closing pressure or the range of action of the switch. The auxiliary spring 49 thus functions to modify the action of the main spring 32 in order to secure accurate performance, and both of the spring adjustments may be conveniently effected with the aid of a screw driver upon removal of the cover 31 and while the switch is in normal use. During adjustment of the main spring 32 the projections 11 of the Washer 13 coact with the grooves 18 to prevent rotation of the washer, and the spring clip 50 also normally prevents rotation of the screw 41.

In order to positively disconnect the .movable contacts 29 from the xed contacts 28, it is only necessary to give the crank 1I of the lever B8 a quarter turn in either direction. Such partial rotation of the crank lever 68 causes the cam 6I to engage the adjacent end of the retaining spring 66 and thereby presses this spring end downwardly against the bottom of the medial recess in the bar member 3|, thus forcing the member downwardly and positively opening both of the movable contacts 29. The contacts 28, 29 will then remain positively separated until the crank lever 68 is again restored to the position shown in Figs. 1, 2 and 5, and such disconnection may be quickly and conveniently. eifected without removing the cover 31. Besides providing a pivot bearing for the lever 68, the leaf CFI spring 66 is formed to positively hold this lever in any adjusted position regardless of the disposition of the switch unit.

From the foregoing detailed description of the construction and operation of my improved pressure actuated toggle switch, it should be apparent that I have in fact provided a switch assemblage which is simple, compact and durable in construction, and which is also highly eicient in operation and flexible in its adaptations. The improved toggle mechanism functions with a snap-action to produce positive impact closing and opening of the contacts; and besides being sensitive and dependable in operation, this toggle may be readily assembled without the use of special fasteners. The loose ts between the toggle plate 2I and the slot 63 of the push-pull member 3l, enables the toggle to build up sufficient momentum when crossing dead center in either direction so as `to cause the member 3I to open and close the contacts 29, 29 with a snap and impact action, and the knifeedge pivot edges of the toggle links eliminate excessive friction, thereby causing the short toggle plate 2| and long flexiblev springs 23 to function with utmost precision. The upward biasing of the resilient contact carrying lingers 30 is also important since it provides contact pressure while the fluid pressure is building up to the tripping point and the force exerted by the toggle upon the contacts approaches and reaches zero value. This biasing of the arms or fingers 30 also prevents fluttering of the contacts, and the use of two toggle springs 23 also augments the flexibility of the improved toggle which has proven highly satisfactory and successful in actual use.

The various essential parts of the improved switch mechanism may also be accurately constructed with the aid of punches and dies. and simple molds; and they may also be easily assembled or dismantled if necessary. The thin flexible retainer 43 cooperates with the stirrup I9 to prevent the same from being swung laterally by the diaphragm I8, and does not unduly interfere with the vertical motion of the stirrup. All parts of the pressure actuated switch are normally well protected while still being quickly accessible for inspection and adjustment, and the adjusting screws 14, 41 afford a wide range of pressure and differential setting and positively maintain such settings with utmost precision. The improved switches due to their extreme simplicity may be manufactured at moderate cost for diverse purposes, and the final assemblages are so compact that they may be readily installed in cramped quarters.

It should be understood that it is not desired to limit this invention to the exact details of construction and operation of the typical pressure actuated toggle switch herein shown and described, for various modifications within the scope of the appended claims may occur to persons skilled in the art.

I claim:

1. In combination, a frame, a rigid lever having one end portion swingably suspended from said frame and also having laterally spaced hooks at its opposite end, means for applying iluid pressure to the medial portion of one face of said lever, an elongated toggle plate having a longitudinal edge swingably cooperable with said hooks, a toggle leaf spring coacting with each of the opposite ends of said toggle plate near said hooks but remote from said edge, the ends of said leaf springs remote from said toggle plate being pivoted on said frame, xed and movable contacts vmountedy on said frame remote from said lever, and a reciprocable member operatively'connecting the swinging portion of said toggle plate with said movable contacts.

2'. In-combination, a frame, a rigid lever having one end portion swingably suspended from said frame and also having laterally spaced hooks plate with said movable contacts, and an adjustable compression spring for applying predetermined pressure to the opposite face of said medial lever portion.

3. In combination, a frame, a rigid lever having one end portion swingably supported on said frameand also having laterally spaced hooks at itsfopposite end, means for applying iluid pressure to the medial portion of the bottom of said lever, an elongated toggle plate having a longitudinal edge swingably cooperable with said hooks, an elongated toggle leaf spring coacting with each of the opposite ends of said toggle plate near said hooks but remote from said edge, the ends of said leaf springs remote from said toggle plate coacting withl said frame, a terminal boa-rd mounted on said frame, iixed and movable contacts carried by said board remote from said lever, and a reciprocable bar member slidable in said frame and said board and operatively connecting the swinging portion of said toggle plate with said movable contacts.

4. In combination, a frame, a rigid lever having one end portion swingably supported on said frame and also having laterally spaced hooks at its opposite end, means for applying iluid pressure to the medial portion of the bottom of said leveran elongated toggle plate having a longitudinal edge swingably cooperable with said hooks, anelongated toggle leaf spring coacting with each of the opposite ends of said toggle plate near said hooks but remote from said edge, the ends of said leaf springs remote from said toggle plate coacting with said frame, a terminal board mounted on said frame, xed and movable contacts carried by said board remote from said lever, a reciprocable bar member guided in said frame and said board and operatively connecting the swinging portion of. said toggle plate with said movable contacts, and an adjustable compression spring interposed between said board and the top of said lever for applying predetermined pressure to the latter.

5. In combination, a frame having opposite side walls and an end wall, avrigid. lever having one end swingably suspended from said side walls and also having laterally spaced hooks at its opposite end, means for applying' uid pressure to the bottom of said lever, an elongated thin toggle plate having a longitudinal edge swingably confined within said hooks, a ileXible toggle leaf spring coacting with each of the opposite ends of saidY toggle plate near said hooks but remote from said edge, the'ends of said leaf springs ree mote from said toggle plate pivtally 'enacting withsaidfene ..wa1l, xed and' movable contacts;

mounted on said frame remote fromsaidlever, and a reciprocable member guided in said frame andoperatively connecting the swinging portion of 'said' toggle 'plate with said movable '\':ontacts.v

6. In'combinaton, a Vframe having spaced side Walls and an intervening end wall, a rigid-lever having one endv swingably suspended from said side walls also having laterally spaced hooks at its opposite end, means-for applying fluid pres'- sure to theV bottom of said lever, an elongated thin toggleV plate having a longitudinal edge swingably coniined within said hooks, ay flexible toggle leaf spring coacting-with eachof the oppositeends ofV saidtoggle plate near said hooks but remote from-said edge, theends of said leaf springs `remote from 'said toggleA plate swingably coacting: with` said end wall,- a terminal board mountedon said side walls,- fixed and movable contactscarriedby said boardlremote from said lever, a reciprocable barmember slidable in said board-and said frame and operatively connectingthe swinging portion of said toggle plate with said movable contacts, andan adjustable compression spring interposed between said board and the top of said lever for applying predetermined pressure to the lever in oppositionto-the fluid pressure.

"7. In combination, afframehavingend sockets, arigid lever having one end portion swingably suspended from saidfframe and also having laterally spaced hooks at its opposite end, means for applying iluidpressure to `one face of said lever, an elongated toggle plate/having a` longitudinal edge swingably confined withinI said hooks, a longitudinally curved toggle leaf spring pivotally confined withinveach of. the opposite ends ofV saidtoggle plate y near said hooks vbut remote from said edge, the ends of said. leaf springs-remote from said toggle plate'beingpiva oted in said sockets andthe opposite endseof each spring beingresiliently biasedtoward. said toggle plate and'sockets, xed and movable oontacts .mounted on Asaid frame remote from said lever, andareciprocable bar member operatively connecting the swingingportion of said toggle plate with said movable-contacts. d

8. In combination, a frame having. side walls provided with notches and an'end wall provided with sockets, a lever having one end swingably confined inthe sidewall notches and also having laterally spaced hooks at its opposite end, meansfor applying iiuid pressure to the bottom of said lever, an elongatedA toggleplate having a longitudinal edge swingably confined within said lever hooks,atoggle leaf spring'pivotally conned within each of the opposite ends oisaid toggle plate near said hooks but remotefrom said edge, the endsof saidvleai springs remote from said toggle plate beingswingably confined within the end wall sockets xed and movable contactsmountedon said frame remote from said lever, and a reciprocable bar member slidably cooperable with said frame and operatively connecting the swinging portion of said toggle plate with said movable contacts.

` tothe bottom of said lever, an elongated-toggle plate havinga--longitudinal edge swingably confined within said lever hooks,- a` toggle leaf spring pivotally conned within-.cacher the opposite l ends` of said toggle platey near: saidhooks..` but remote frein said edge, the" ends of said-leaf,y

springs remote from said toggle plate being swingably associated with said frame, vixed and movable contacts mounted on said frame remote from said lever, and a reciprocable bar member slidably cooperable with said frame and loosely connecting the swinging portion of said toggle plate with said movable contacts.

10. In combination, a frame, a rigid lever having one end portion swingably supported on said frame and also having laterally spaced hooks at its opposite end, means for applying fluid pressure to the medial portion of said lever, an elongated toggle plate having a longitudinal pivot edge swingably cooperable with said hooks and being provided with a central projection on its opposite edge, an elongated toggle leaf spring coacting with each of the opposite ends of said toggle plate near said opposite edge but remote from said pivot edge, the ends of said leaf springs remote from said toggle plate pivotally coacting with said frame, fixed and movable contacts carried by said frame remote from said lever, and a reciprocable bar member slidable in said frame and said board and loosely connecting the projection on said toggle plate with said movable contacts.

l1. In combination, a frame, a rigid lever pivotally suspended from the frame and having laterally spaced hooks remote from its pivots, means for applying fluid pressure to said lever between the pivots and hooks, an elongated rigid toggle plate having a pivot edge swingably cooperable with said hooks and also having a projection at its swinging opposite edge, an elongated toggle leaf spring coacting with each of the oppositeends of said toggle plate near said opposite edge but remote from said pivot edge, the ends of said leaf springs remote from said toggle plate pivotally coacting with said frame, a terminal board mounted on said frame, ved contacts secured to said board, movable contacts carried by leaf springs secured to said board and biased toward said fixed contacts, and a reciprocable bar member guided in said frame and said board and having a slot loosely coacting with said toggle plate projection and with said contact carrying springs.

12. In combination, a frame having sockets, a rigid lever having pivots swingably suspended from said sockets and also having hooks remote from said pivots, means for applying iiuid pressure to said lever, a rigid toggle plate having a knife edge pivoted within said hooks, an elongated flexible toggle leaf spring pivotally conned within each of the opposite ends of said toggle plate remote from said pivot edge and coacting with said frame. xed and movable contacts supported upon said frame remote from said lever, and a reciprocable bar member loosely connecting the swinging medial portion of said toggle plate with said movable contacts.

13. In combination, a frame, a rigid lever swingably suspended from said frame, means for applying pressure to said lever to swing the same, a terminal board mounted upon said frame remote from said lever, xed and movable contacts carried by said terminal board, a toggle operable by said lever, a reciprocable bar slidable in said frame and said terminal board and operatively connecting said toggle with said movable contacts, an angular leaf spring element having one end portion secured to said terminal board and a second end portion cooperable with an end of said bar, and a cam member lournaled in the medial portion of said springr ele-4 Vl2 ment and coactlng with said bar through said second end portion to maintain said movable contacts open in opposition to said toggles.

14. In combination, a frame, a rigid lever swingably suspended from said frame, means for applying pressure to said lever to swing the same, a terminal board mounted upon said frame remote from said lever, fixed and movable contacts carried by said terminal board, a dual link toggle interposed between said frame and said lever and having one link provided with a projection extending beyond the connection between its links, and a bar slidable within said frame and said terminal board and having slots loosely coacting with said link projection and with said movable contacts.

l5. In combination, a frame, a rigid lever swingably suspended from said frame, means for applying pressure to said lever to swing the same, a terminal board mounted upon said frame remote from said lever, Xed and movable contacts carried by said terminal board, said movable contacts being carried by resilient arms biased toward the xed contacts, a toggle interposed between said frame and said lever and having a link plate provided with a swinging projection, and a reciprocable bar having slots loosely coacting with said arms and with said link projection.

16. In combination, a frame, a rigid lever having one end portion swingably suspended from said frame and being provided with a hook at its opposite end, means for applying fluid pressure to the medial portion of said lever, a toggle plate having a knife edge swingably cooperable with said hook, medially curved toggle leaf spring having one oiT-set end coacting with said toggle plate near said hook but remote from said knife edge, the opposite end of said toggle leaf spring also being off-set and having knife edge pivotal coaction with said frame, fixed and movable 'contacts mounted on said frame, and a reciprocable member operatively connecting a swinging portion of said toggle plate opposite from said knife edge with said movable contact.

17. In combination, a frame, a rigid lever having one end portion swingably suspended from said frame and being provided with a hook at its opposite end, means for applying uid pressure to the medial portion of one face of said lever, a toggle plate having a knife edge swingably cooperable with said hook, a medially curved toggle leaf spring having one off-set end pivotally coactingr with said toggle plate near said hook but remote from said knife edge, the opposite end of said toggle leaf spring also being off-set and having knife edge coaction with said frame, iixed and movable contacts mounted on said frame, a reciprocable member operatively connecting a swinging portion of said toggle plate opposite from said knife edge with said movable contact, and an. adjustable spring for applying predetermined pressure to the Opposite face of said medial rigid lever portion.

18. In combination, a frame, a rigid lever having one end portion swingably suspended from said frame and being provided with a hook at its opposite end, means for applying iluid pressure to the medial portion of one face of said lever. a teerde plate having a knife edge swingably coonerable with said hook, a medially curved mggleleef spring having one off-set end pivotally coacting with said toggle plate near said hook biet' remote from said knife edge, the-oppo site end of said toggle leaf spring also being off- 2,598,586 13 14 set and having knife edge coaction with said REFERENCES CITED frame, a terminal board mounted on said frame, The following references are of record in the xed and movable contacts carried by said board, me of this patent: a reoiprocable bar member slidable in said frame and said terminal board and operatively con- 5 UNITED STATES PATENTS necting a swinging portion of said toggle plate Number Name Date opposite from said knife edge with said movable 2,193,127 Furnas et al Mar. 12, 1940 Contact, and adjustable means for applying pre- 2,194,128 Shaw Mar. 19, 1940 determined pressure to the opposite face of said 2,307,265 Hansen Jan. 5. 1943 medial rigid lever portion. lo 2,453,861 Rothwell Nov. 16, 1948 GILBERT H. HANSEN. 

